Technical Field
The present invention relates to a novel precursor compound and a film deposition method using the same, as a tungsten precursor suitable for use in chemical vapor deposition or atomic layer deposition, which is a deposition process that can be used to form dielectric films in semiconductor devices as organic metals.
Background Art
Chemical vapor deposition (CVD) and atomic layer deposition (ALD) have been applied as techniques for the deposition of thin films for semiconductor devices because they can achieve conformal films (metals, oxides, nitrides, etc.) through fine tuning of parameters during the process. Since film growth is mainly controlled by the chemical reaction of metal-organic compounds (precursors), it is important to develop optimal precursors by predicting their properties and reaction processes. Thus, efficient precursors have been developed to achieve specific properties for certain types of films.
Precursors are molecules for CVD and ALD processes and some of their unique properties must be considered before using them. First, liquid form and/or sufficient vapor pressure are required to facilitate transport of gaseous precursors from the containing vessel into the reaction chamber. Second, long-term thermal stability is required in storage conditions and transport conditions, and gas phase thermal stability is also necessary to prevent impurities from entering the film. Third, strong reactivity to reactive gases, such as ammonia or oxygen, is required to readily convert precursors to the required film on a sample substrate. Another important requirement to be considered for the precursor in the precursor design phase is to remove impurities from the film from the ligand during the deposition process.
Tungsten is used in a variety of applications that are useful in fabricating nano-devices. Deposition of pure tungsten may be used to fill the holes (“contact holes”) that make the junctions to the transistor source and drain, or to fill the bias between successive layers of metal. This approach is known as the “tungsten plug” process. With WF6, due to the good nature of the deposited film, the utilization of tungsten can be diversified. However, it is necessary to provide an adhesion/barrier layer, for example Ti/TiN, in order to protect the underlying Si by infiltration with fluorine, or to ensure the adhesion of tungsten to silicon dioxide.
Tungsten-silicide can be used to increase the conductivity of the gate line on top of the polysilicon gate and thus increase the transistor speed. This method is widely used in DRAM fabrication. The gate at this time is a word line for the circuit. Although WF6 and SiH4 can be used, dichlorosilane (SiCl2H2) is more commonly used as a silicon source, because it allows higher deposition temperatures and thus results in lower fluorine concentrations in deposited films.
Tungsten nitride (WNx) is considered a good barrier to copper diffusion in microelectronic circuits. WNx can also be used for electrodes for thin-film capacitors and field-effect transistors.
WF6 can be used to deposit pure tungsten films in CVD mode using H2 at high temperatures because of the W6+ oxidation state of liquid and highly volatile (Applied Surface Science, 73, 1993, 51-57; Applied Surface Science, 78, 2, 1994, 123-132). WF6 can also be used in CVD mode in combination with silane for the production of tungsten silicide films at low temperatures.(Y. Yamamoto et al. Proc. Int. Conf. on CVD-XIII (1996) 814;Surface Science 408 (1998) 190-194). However, WF6 is limited by the high thermal budget required for the deposition of pure tungsten film or due to fluorine which causes etching of the underlying silicon surface.
W(CO)6 can be used for the deposition of pure tungsten or tungsten nitride films in CVD mode due to WO oxidation state. But it was limited to mass production due to its high toxicity. (Kaplan et al., J. Electrochem. Soc. 1979, 117, 693; Sun et al Thin Solid Films 2001, 397, 109)
W(CO)2(1,3-butadiene)2 can be used in the CVD mode, but deposition of a tungsten carbide film is formed. (Jipa et al., Chemical Vapor Deposition 2010, 16 (7-9), 239)
However, the W6+ oxidation state in the biscyclopentadienyl tungsten precursor with the formula W(RCp)2H2 can be used in the CVD mode for the deposition of pure tungsten, but a high deposition temperature is required resulting in carbon contamination. (Zinn et al Adv Mater. 1992, 375; Spee et al Mat. Sci. Eng 1993 (B17) 108; Ogura et al J. of Vac. Sci. Tech. 2008, 26, 561)
U.S. Pat. No. 7,560,581 B2 discloses the use of bis-alkylimido bis-dialkylamino tungsten precursors for the production of tungsten nitride in ALD mode with or without copper barrier diffusion applications.
Several diazabutadiene molecules have been developed apart from the tungsten precursor mentioned above. Diazabutadiene (DAD) ligands are diamine ligands that can be used under different oxidation states.
U.S. Pat. No. 7,754,908 to Reuter et al. discloses the use of bis-alkylimido diazabutadiene tungsten precursors for the production of tungsten-containing films. However, the use of an alkyl imido group has the disadvantage that introduction of carbon into the resulting film is possible. The tungsten molecule may contain several kinds of ligands other than homologous ligands. Therefore, their synthesis takes place in several stages, and the complexity, difficulty, and the like of the synthesis eventually lead to an increase in cost.
WO2012/027357 of Winter discloses a method of forming a thin film on a substrate comprising step of contacting the surface with a precursor compound having a transition metal and at least one alkyl-1,3-diazabutadiene ligand.
The deposition of a tungsten-containing film (pure tungsten, tungsten nitride or tungsten silicide) in the CVD or ALD mode can be problematic due to high C, O or F content in the film. Thus, a tungsten-containing precursor suitable for CVD or ALD deposition processes is needed. Preferred properties of tungsten-containing precursors for these applications are: i) liquid form or low melting point solids; ii) high volatility; iii) thermal stability to avoid degradation during handling and transportation; and iv) appropriate reactivity during the CVD/ALD process; and v) a pure tungsten film should be deposited in CVD or ALD (thermal or plasma mode) at a temperature of less than 200, preferably less than 150, and the thermal stability should not be too high to permit deposition at low temperatures.